KR101324437B1 - System for clarifying exhaust gas of direct injection engines and control method thereof - Google Patents

Abstract

The present invention relates to an exhaust gas purification system for a gasoline ultra-lean combustion direct injection engine and a control method thereof.

The present invention is a fuel reformer for selectively supplying the reformed fuel gas to the NSC and the NSC in the UCC, and the heat exchanger for controlling the temperature of the switch valve and the NSC and supplying heat to the fuel reformer. An exhaust gas purification system and a cold start section of a gasoline ultra-lean combustion direct injection engine, and a method for controlling the exhaust gas purification system in an engine driving or regeneration section of an NSC are provided.

According to the present invention, in the exhaust gas purification system of a gasoline ultra-lean combustion direct injection engine, the TWC is placed in the NCC and the rear end of the NSC in the UCC, and the NSC and the TWC are activated using the fuel reformer, the switch valve, and the heat exchanger. By early reaching the temperature for and maintaining a sufficient reduction state during NSC regeneration, it has the effect of improving the fuel efficiency of the engine and strengthening the purification function of the exhaust gas purification system.

Direct injection engine, three-way catalyst, nitrogen oxide storage catalyst, fuel reformer, TWC, NSC, CCC, UCC

Description

System for clarifying exhaust gas of direct injection engines and control method

The present invention relates to an exhaust gas purification system for a gasoline ultra-lean combustion direct injection engine and a control method thereof. More specifically, the position of the TWC at the rear end of the NSC and the NSC in the UCC, the fuel reformer for selectively supplying the reformed fuel gas to the NSC or TWC, the heat exchanger for controlling the temperature of the switch valve and NSC and supplying heat to the fuel reformer The present invention relates to a method for controlling an exhaust gas purification system and a cold start section of a gasoline ultra-lean combustion direct injection engine composed of a gas and a regeneration section of an engine driving or NSC.

The biggest issue in the development of gasoline engines is to improve the performance by optimizing the efficiency of the powertrain system, which consists of the engine and the exhaust gas purification system.

In the future, global warming regulations are expected to be tightened. In particular, strong regulations will be applied to automobile exhaust, which is the main cause of CO2 emissions. To cope with this, the automotive industry is responding to global warming regulations in gasoline powertrain systems by minimizing air pollution by optimizing engine performance and optimizing exhaust gas purification system.

Among the gasoline powertrain systems currently in development or in production, the technology to improve down-sizing and fuel efficiency of the engine is a gasoline direct injection engine. The gasoline direct injection engine can increase the thermal efficiency and volumetric efficiency by directly injecting fuel into the cylinder as compared to the conventional port fuel injection, and implements lean or ultra-lean combustion using less fuel, which is about 20% engine. It is a system that can increase fuel economy. In addition, by applying the nitrogen oxide purification mechanism can satisfy both fuel economy regulation and exhaust gas regulation at the same time.

The ultra-thin combustion direct injection engines currently under development are difficult to purify the exhaust gases from the engine with only three-way catalyst (TWC). NSC) further. In other words, the TWC is mounted in a closed-coupled converter (CCC), which is the rear end of the ultra-lean combustion direct injection engine, and the NSC is installed in the underfloor coupled converter (UCC). The gas regulation is satisfied (FIG. 1).

However, the powertrain system equipped with NSC in UCC reduces fuel economy by about 5% to 10% due to the operation of NSC. As a result, the powertrain system consisting of ultra-lean combustion direct injection engine increases fuel efficiency by about 10-15%. You can only see the effect. In addition, the typical active temperature range of NSC is 250 ° C. to 400 ° C. (optimal active temperature is around 300 ° C.), which is lower than the TWC's typical active temperature range of 400 ° C. to 800 ° C. (optimal active temperature is around 600 ° C.) In order to remove nitrogen oxides stored in the gas, there is a problem in that the amount of carbon dioxide or hydrocarbon which is a reducing agent is increased by making it richer than the theoretical performance ratio. In addition, since the TWC is mounted on the front end of the NSC, the carbon monoxide or hydrocarbon, which acts as a reducing agent in the regeneration of NSC, is preliminarily purified from the TWC, thereby making NSC regeneration efficiency worse.

When the NSC is mounted at the CCC position and the TWC is mounted at the rear end of the NSC which is the UCC position, carbon dioxide or hydrocarbons contained in the gas discharged from the engine is used as a reducing agent in the NSC. In general, NSC cannot be used at CCC location because its deterioration in deterioration at temperatures above 400 ° C, and TWC is relatively fast at light-off temperature (LOT) in order to meet the stricter emission regulations. It must be reached and used at the CCC location.

Accordingly, the present invention has been invented to solve this problem, and the position of the TWC at the rear end of the NSC and the NSC in the UCC, and the temperature of the fuel reformer, switch valve and NSC for selectively supplying the reformed fuel gas to the NSC or TWC It provides an exhaust gas purification system for gasoline ultra-lean combustion direct injection engines and a control method thereof, which is composed of a heat exchanger for controlling and supplying heat to the fuel reformer, thereby facilitating temperature control for activation of NSC and TWC, and By maintaining the reduced state, the object is to improve the fuel economy of the engine and to enhance the purification function of the exhaust gas purification system.

The present invention, NSC and TWC located in the rear end of the NSC; A fuel reformer connected in the direction of the exhaust gas purification system in the fuel tank, driven separately from the engine, for supplying reformed fuel gas to the NSC or TWC; A switch valve located at the rear of the fuel reformer and above the NSC and the TWC, for selectively supplying the reformed fuel gas to the NSC or the TWC; And a heat exchanger positioned on the NSC and the fuel reformer. The exhaust gas purification system of the gasoline ultra-lean combustion direct injection engine is provided.

In another aspect, the present invention, the first step to determine whether the activation of the TWC by measuring the temperature of the cooling water or intake air after starting; A second step of operating the switch valve toward the fuel reformer, the heat exchanger, and the TWC when the first step requires activation of the TWC; A third step of determining whether lean combustion; And a fourth step of terminating the activation of the TWC by not operating the switch valve when the lean combustion is performed in the third step. It provides a method for controlling the exhaust gas purification system in the cold start section, characterized in that consisting of.

In another aspect, the present invention, the first step of determining whether the engine is in lean combustion if the operating conditions; A second step of measuring the temperature of the NSC in the case of lean combustion in the first step; A third step of opening the switch valve toward the NSC when the temperature of the NSC is less than 300 ° C. in the second step to supply reformed fuel gas and to measure the temperature of the NSC; And a fourth step of closing the switch valve and operating the heat exchanger when the temperature of the NSC exceeds 300 ° C. in the third step. It provides a method for controlling the exhaust gas purification system in the regeneration section of the engine drive or NSC, characterized in that consisting of.

According to the present invention, in the exhaust gas purification system of a gasoline ultra-lean combustion direct injection engine, the TWC is placed in the NCC and the rear end of the NSC in the UCC, and the NSC and the TWC are activated using the fuel reformer, the switch valve, and the heat exchanger. By early reaching the temperature for and maintaining a sufficient reduction state during NSC regeneration, it has the effect of improving the fuel efficiency of the engine and strengthening the purification function of the exhaust gas purification system.

According to the present invention, it is possible to reduce the fuel consumption deterioration of 5 to 10%, which is a problem in the existing NSC-powered powertrain system, to within 5%, and to install the fuel reformer driven separately from the engine to provide an engine and exhaust gas purification system. Independent operation can improve the efficiency of the powertrain system.

The present invention provides an exhaust gas purification system for a gasoline ultra-lean combustion direct injection engine, comprising: an NSC (10) and a TWC (20) positioned at the rear end of the NSC; A fuel reformer 50 connected to the exhaust gas purification system in the fuel tank 30 and driven separately from the engine 40 to supply reformed fuel gas to the NSC or the TWC; A switch valve 60 positioned at the rear of the fuel reformer and above the NSC and the TWC, for selectively supplying the reformed fuel gas to the NSC or the TWC; And a heat exchanger 70 positioned above the NSC and the fuel reformer.

In another aspect, the present invention, a method for controlling the exhaust gas purification system in the cold start section, the first step of determining whether the TWC needs to be activated by measuring the temperature of the cooling water or intake air after starting; A second step of operating the switch valve toward the fuel reformer, the heat exchanger, and the TWC when the first step requires activation of the TWC; A third step of determining whether lean combustion; And a fourth step of terminating the activation of the TWC by not operating the switch valve when the lean combustion is performed in the third step. It provides an exhaust gas purification system control method comprising the.

The present invention also provides a method for controlling an exhaust gas purification system in an engine driving or regeneration section of an NSC, comprising: a first step of determining whether lean combustion is performed when an engine is in an operating condition; A second step of measuring the temperature of the NSC in the case of lean combustion in the first step; A third step of opening the switch valve toward the NSC when the temperature of the NSC is less than 300 ° C. in the second step to supply reformed fuel gas and to measure the temperature of the NSC; And a fourth step of closing the switch valve and operating the heat exchanger when the temperature of the NSC exceeds 300 ° C. in the third step. It provides an exhaust gas purification system control method comprising the.

The present invention also provides a method for controlling an exhaust gas purification system in an engine driving or regeneration section of an NSC, comprising: a first step of determining whether lean combustion is performed when an engine is in an operating condition; Determining whether regeneration of the NSC is necessary in case of ultra-lean combustion in the first step; Opening the switch valve toward the NSC when regeneration of the NSC is required, supplying the reformed fuel gas and checking whether the NSC is regenerated; And not operating the switch valve when the NSC is regenerated; It provides an exhaust gas purification system control method characterized in that.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Figure 2 is a block diagram showing an exhaust gas purification system of the ultra-thin combustion direct injection engine of the present invention.

As shown in FIG. 2, the exhaust gas purification system of the gasoline ultra-lean combustion direct injection engine of the present invention includes an NSC 10 and a TWC 20 positioned at the rear end of the NSC; A fuel reformer 50 connected to the exhaust gas purification system in the fuel tank 30 and driven separately from the engine 40 to supply reformed fuel gas to the NSC or the TWC; A switch valve 60 positioned at the rear of the fuel reformer and above the NSC and the TWC, for selectively supplying the reformed fuel gas to the NSC or the TWC; And a heat exchanger (70) located between the engine (40) and the NSC (10) and between the engine (40) and the fuel reformer (50). .

According to the present invention, by mounting the TWC at the rear end of the NSC, the carbon monoxide or hydrocarbon contained in the gas discharged from the engine during NSC regeneration can be used as a reducing agent, and as a result, the performance of the NSC regeneration can be improved.

The NSC and TWC of the present invention are preferably located in the UCC. By installing both NSC and TWC inside the UCC, the space of the engine room can be increased, and various parts can be easily arranged in the engine, and the engine efficiency can be maximized by securing independent operation of the exhaust gas purification system.

The heat exchanger of the present invention controls the temperature of the NSC to the active temperature range, and serves to adjust the intake air temperature supplied to the fuel reformer. The shape of the heat exchanger is not particularly limited, but it is preferable to use an air-cooled heat exchanger. In order to improve the performance of the fuel reformer, high temperature intake air is generally required, which can be achieved by supplying the fuel reformer with hot air discharged from an air cooled heat exchanger.

The heat exchanger is preferably characterized in that to supply the NSC by adjusting the temperature of the engine exhaust gas to 250 ℃ ~ 400 ℃. The efficiency of NSC can be maximized by adjusting the temperature of engine exhaust gas to 250 ℃ ~ 400 ℃ which is the active temperature range of NSC.

The heat exchanger is preferably characterized in that to transfer the heat of the engine exhaust gas to the fuel reformer. The energy loss can be minimized by supplying the fuel reformer with the amount of heat obtained while adjusting the temperature of engine exhaust gas to 250 degreeC-400 degreeC.

The fuel reformer of the present invention is connected to the exhaust gas purification system in the fuel tank, is driven separately from the engine, and serves to supply reformed fuel gas to the NSC or TWC. In addition, the present invention can be selectively supplied to the reformed fuel gas to the NSC or TWC by installing the rear end of the fuel reformer and the upper switch valve of the NSC and TWC.

The reformed fuel gas supplied to the NSC is preferably characterized by having hydrogen and carbon monoxide as main components. The reformed fuel gas emitted from the fuel reformer generally consists of hydrogen, carbon monoxide, and hydrocarbons. Among them, hydrogen and carbon monoxide have a fast reduction reaction rate with NOx, and the reaction occurs at low temperature, thereby maximizing NSC purification efficiency by supplying NSC with reformed fuel gas mainly composed of hydrogen and carbon monoxide.

The present invention is preferably characterized by maintaining the temperature of the NSC at 250 ° C to 400 ° C by supplying the reformed fuel gas to the NSC. In particular, in the cold start section, the NSC generally forms a temperature lower than the catalyst activation temperature of 250 ° C. to 400 ° C., and the temperature of the NSC may be maintained at 250 ° C. to 400 ° C. by supplying the hot reformed fuel gas to the NSC.

Preferably, the present invention is characterized in that the temperature of the TWC is maintained at 400 ° C. to 800 ° C. by mixing the reformed fuel gas with the gas discharged from the NSC and supplying it to the TWC. In addition, the present invention is characterized in that the temperature of the TWC is maintained at 400 ℃ ~ 800 ℃ within 30 seconds of the cold start in the cold start section. In the present invention, since the TWC is located at the rear end of the NSC, there may be a problem in the early activation of the catalyst, especially at the beginning of cold start. Existing exhaust gas purification systems place the TWC as close as possible to the engine exhaust manifold and use the high temperature exhaust gases from the engine to induce early activation of the TWC. In the present invention, in order to induce early activation of the TWC, the temperature of the TWC is maintained at 400 ° C. to 800 ° C. by supplying a high-temperature reforming fuel gas to the gas discharged from the NSC and supplying it to the TWC. Since the reformed fuel gas has a temperature of about 1000 ° C., it is possible to induce rapid early activation of the catalyst even when it is mixed with the gas emitted from the NSC and supplied to the TWC. It is possible to induce the activity of the catalyst by maintaining the temperature of the TWC at 400 ℃ ~ 800 ℃ within seconds.

3 is a flowchart illustrating a method of controlling the exhaust gas purification system of the present invention in a cold start section, and FIG. 4 is a flowchart illustrating a method of controlling the exhaust gas purification system of the present invention in an engine driving or regeneration section of an NSC.

Here, T_Cool refers to the temperature of the cooling water and T_Air refers to the temperature of the intake air. POS_V = 0 means the switch valve is not actuated, POS_V = 1 means the switch valve opens to the TWC side, and POS_V = 2 means the switch valve opens to the NSC side. The state in which the switch valve is not operated means a state in which the reformed fuel gas is not supplied to the TWC and NSC by closing the switch valve. LV_REFM = 0 means that the fuel reformer is not running and LV_REFM = 1 means running the fuel reformer. LV_HTX = 0 means that the heat exchanger is not in operation, and LV_HTX = means that the heat exchanger is in operation.

The exhaust gas purification system in which the TWC is located at the rear end of the NSC of the present invention requires control of two sections for the efficient operation of the system, unlike the exhaust gas purification system in which the NSC is located at the rear of the NSC. The control system for implementing the control method of the present invention does not require an additional control system because it can be configured by changing the existing Lean NOx Trap (LNT) control method.

In general, since the cold start section is not driven by lean burn, it adversely affects the activation of the catalyst and implements lean burn after the warm-up of the catalyst. The method of controlling the exhaust gas purification system in the cold start section is as follows.

As shown in FIG. 3, the method for controlling the exhaust gas purification system in the cold start section of the present invention first determines whether the TWC needs to be activated by measuring the temperature of the cooling water or the temperature of the intake air after starting (S100). . The temperature of the cooling water (T_Cool) or the temperature of the intake air (T_air) is a major factor in determining whether NSC or TWC activity is required. When activation of the TWC is required to operate the switch valve toward the fuel reformer, the heat exchanger, and the TWC (S120), and if the activation of the TWC is not necessary, the fuel reformer, the heat exchanger, and the switch valve are not operated (S160). When activation of the switch valve toward the fuel reformer, the heat exchanger, and the TWC is required to activate the TWC, it is determined whether the lean burn is finished (S130). In the case of implementing lean combustion, the switch valve is not operated (S140) and the catalyst activation is terminated (S150). If the lean burn is not implemented, the switch valve is opened toward the TWC to supply the reformed fuel gas and promote the activity of the TWC (S170). At the same time as supplying the reformed fuel gas, the catalyst bed temperature is configured as a calibration table (S180) to check whether the activity and temperature (Light Off Temperature, LOT) of the TWC have been reached (S190). When the activation temperature of the TWC is reached, the switch valve is not operated to terminate the activation of the TWC (S200), and after the theoretical air-fuel ratio operation is completed, normal lean combustion is realized. When the activation temperature of the TWC has not been reached, the lean burn determination step is repeated.

The method for controlling the exhaust gas purification system in the cold start section of the present invention can promote the activation of the TWC to improve the purification efficiency of the exhaust gas.

The method for controlling the exhaust gas purification system in the regeneration section of the engine driving or NSC of the present invention is as follows.

As shown in FIG. 4, the method for controlling the exhaust gas purification system in the regeneration section of the engine driving or NSC according to the present invention first determines whether lean combustion is present under operating conditions (S300). In the case of lean combustion, the temperature of the NSC is measured, and it is determined whether the temperature of the NSC is less than 300 ° C. (S310). If the temperature of the NSC exceeds 300 ℃, do not operate the switch valve (S350), if the temperature of the NSC is less than 300 ℃ to open the switch valve to the NSC to supply reformed fuel gas (S320) and to measure the temperature of the NSC again It is determined again whether or not less than 300 ℃ (S330). When the temperature of the NSC is measured again, when the temperature of the NSC exceeds 300 ° C, the switch valve is closed and the heat exchanger is operated (S340). When the temperature of the NSC is less than 300 ° C, the switch valve is opened to the NSC to supply reformed fuel gas. Step S320 is performed again.

Meanwhile, as a result of determining whether lean combustion is performed (S300), in the case of ultra lean combustion, the method of controlling the exhaust gas purification system in the engine driving or regeneration section of the NSC of the present invention first determines whether the regeneration of the NSC is necessary (S360). . When the regeneration of the NSC is necessary, the switch valve is opened to the NSC to supply the reformed fuel gas (S370), and the regeneration of the NSC is checked (S380). In the step S360 of determining whether the regeneration of the NSC is necessary, the switch valve is not operated when the regeneration of the NSC is not necessary (S400). When the NSC is not played back in the step of checking whether the NSC is played (S380), the process of determining whether the NSC is required to be played back is performed again (S360).

According to the method of controlling the exhaust gas purification system in the engine driving or regeneration section of the NSC of the present invention, when the regeneration of the NSC is not necessary, all sections can be driven to the ultra-thin combustion zone, thereby greatly improving fuel economy. have.

In addition, when driven into a lean burn zone, the NSC temperature is monitored and maintained at 300 ° C. to optimize the occlusion efficiency of the NSC. This can reduce the temperature of the NSC by operating the heat exchanger when the temperature of the NSC exceeds 300 ° C and reduce the temperature of the gas discharged from the engine, or operate the switch valve toward the fuel reformer and NSC when the temperature of the NSC is below 300 ° C. It can be achieved by a control method for increasing the temperature of the NSC by supplying a high-temperature reformed fuel gas to the NSC.

In addition, when the regeneration of the NSC is necessary, the switch valve is operated toward the fuel reformer and the NSC, and the reforming time of the NSC is shortened by supplying the reformed fuel gas to the NSC. This ultimately constitutes a control method that can reduce the fuel economy that occurs during NSC regeneration and improve NSC regeneration.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a block diagram showing an exhaust gas purification system of a conventional ultra-thin combustion direct injection engine.

Figure 2 is a block diagram showing an exhaust gas purification system of the ultra-thin combustion direct injection engine of the present invention.

3 is a flowchart illustrating a method of controlling the exhaust gas purification system of the present invention in a cold start section, and FIG. 4 is a flowchart illustrating a method of controlling the exhaust gas purification system of the present invention in an engine driving or regeneration section of an NSC.

Description of the Related Art

10: NSC 20: TWC

30: fuel tank 40: engine

50: fuel reformer 60: switch valve

70: Heat exchanger

Claims (15)

In the exhaust gas purification system of a gasoline ultra thin combustion direct injection engine, A NOx Storage Catalyst (NSC) 10 and a Three Way Catalyst (TWC) 20 positioned after the NOx storage catalyst; A fuel reformer 50 connected to the exhaust gas purification system in the fuel tank 30 and driven separately from the engine 40 to supply reformed fuel gas to the nitrogen oxide storage catalyst or the three-way catalyst; A switch valve 60 positioned at the rear of the fuel reformer and at the top of the nitrogen oxide storage catalyst and the three-way catalyst, for selectively supplying the reformed fuel gas to the nitrogen oxide storage catalyst or the three-way catalyst; And And a heat exchanger (70) positioned between the engine and the nitrogen oxide storage catalyst and between the engine and the fuel reformer. The method of claim 1, And the nitrogen oxide storage catalyst and the three-way catalyst are located in an Under-Floor Coupled Converter (UCC). The method according to claim 1 or 2, The heat exchanger is an exhaust gas purification system, characterized in that for supplying to the nitrogen oxide storage catalyst by adjusting the temperature of the engine exhaust gas to 250 ℃ ~ 400 ℃. The method according to claim 1 or 2, The heat exchanger exhaust gas purification system, characterized in that for transmitting the heat of the engine exhaust gas to the fuel reformer. The method according to claim 1 or 2, The reformed fuel gas supplied to the nitrogen oxide storage catalyst comprises hydrogen and carbon monoxide as main components. The method according to claim 1 or 2, And the exhaust gas purification system maintains the temperature of the nitrogen oxide storage catalyst at 250 ° C to 400 ° C by supplying the reformed fuel gas to the nitrogen oxide storage catalyst. The method according to claim 1 or 2, The exhaust gas purification system is characterized by maintaining the temperature of the three-way catalyst to 400 ℃ ~ 800 ℃ by mixing the reformed fuel gas with the gas discharged from the nitrogen oxide storage catalyst to supply to the three-way catalyst. 8. The method of claim 7, The exhaust gas purification system, the exhaust gas purification system, characterized in that to maintain the temperature of the three-way catalyst 400 ℃ ~ 800 ℃ within 30 seconds cold start in the cold start section. A method for controlling the exhaust gas purification system of claim 1 or 2 in a cold start section, A first step of determining whether activation of the three-way catalyst is necessary by measuring the temperature of the cooling water or the intake air after starting; A second step of operating the switch valve toward the fuel reformer, the heat exchanger, and the three-way catalyst when activation of the three-way catalyst is required in the first step; A third step of determining whether lean combustion; And A fourth step of terminating the activation of the three-way catalyst by not operating the switch valve in the case of lean combustion in the third step; An exhaust gas purification system control method, characterized in that consisting of. 10. The method of claim 9, And not operating the fuel reformer, the heat exchanger, and the switch valve when activation of the three-way catalyst is not necessary in the first step. The method of claim 10, Opening the switch valve toward the three-way catalyst when the lean combustion is not performed in the third step, supplying the reformed fuel gas and checking whether the three-way catalyst activity and temperature are reached; And not operating the switch valve when the activation temperature is reached in the step of confirming whether the activation temperature of the three-way catalyst is reached, and performing the third step when the activation temperature is not reached. Exhaust gas purification system control method. A method of controlling the exhaust gas purifying system of claim 1 or 2 in an engine driving or regeneration section of a nitrogen oxide storage catalyst, A first step of determining whether lean combustion occurs when the engine is in an operating condition; A second step of measuring the temperature of the nitrogen oxide storage catalyst when the lean combustion is performed in the first step; A third step of opening the switch valve toward the nitrogen oxide storage catalyst to supply the reformed fuel gas and measuring the temperature of the nitrogen oxide storage catalyst when the temperature of the nitrogen oxide storage catalyst is less than 300 ° C in the second step; And A fourth step of closing the switch valve and operating the heat exchanger when the temperature of the nitrogen oxide storage catalyst in the third step exceeds 300 ° C; An exhaust gas purification system control method, characterized in that consisting of. 13. The method of claim 12, Not operating the switch valve when the temperature of the nitrogen oxide storage catalyst in the second step exceeds 300 ° C; And Performing the third step when the nitrogen oxide storage catalyst is less than 300 ° C. in the third step; Exhaust gas purification system control method further comprising. 14. The method of claim 13, Determining whether regeneration of the nitrogen oxide storage catalyst is necessary in the case of ultra-lean combustion in the first step; If the regeneration of the nitrogen oxide storage catalyst is necessary, opening the switch valve toward the nitrogen oxide storage catalyst to supply a reformed fuel gas and confirming whether the nitrogen oxide storage catalyst is regenerated; And Not operating the switch valve when the nitrogen oxide storage catalyst is regenerated; Exhaust gas purification system control method further comprising. 15. The method of claim 14, Not operating the switch valve when the regeneration of the nitrogen oxide storage catalyst is not necessary in the step of determining whether regeneration of the nitrogen oxide storage catalyst is necessary; And Determining whether regeneration of the nitrogen oxide storage catalyst is necessary when the nitrogen oxide storage catalyst is not regenerated in the step of checking whether the nitrogen oxide storage catalyst is regenerated; Exhaust gas purification system control method further comprising.

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